The present invention relates to a drum winder for winding a web, which comprises winding drums that support a roll that is being formed and a pressurized gap formed by the winding drums and by the roll that is being formed.
The present invention also relates to a method for winding a web in a drum winder in which the web is wound onto a roll supported by winding drums.
In drum winding, it is desirable to lower the linear nip loads produced by the weight of the growing roll, because otherwise the linear loads that act in the nips will become excessively high, causing defects in the roll.
With respect to the prior art, reference is made to the publications DE 1,047,001, DE 1,111,496, DE 3,618,955, and U.S. Pat. No. 3,497,151. In the devices described in these prior art references, it is known to pass a pressure into the gap formed by the roll that is being formed and by the winding drums, whereby a relief effect is applied to the roll that is formed. As a result of this effect, the linear loads in the nips cannot become excessively high. In order that the pressure should be retained in the gap formed by the roll and by the winding drums, it is known from the prior art to seal the gap from above and from below, respectively, by means of various sealing constructions. From the publication DE 1,047,001, it is known to move the upper roll-end sealing unit in an axial direction of the roll.
In addition, from U.S. Pat. No. 3,346,209, it is known to regulate the pressure present in the gap formed by the roll and the winding drums by moving the lower drum in a substantially vertical direction, i.e., up and down.
Even though by means of the prior art devices described above, considerable improvement in the winding of a web onto a roll is achieved, they involve certain drawbacks. For example, sealing of the gap formed by the roll that is formed and the winding drums is generally problematic. The pressure always leaks to some extent, which results in problems of dust formation. Owing to the leakage of the pressure, a very large quantity of air is needed to maintain the pressure, which air spreads into the working environment, for which reason the dust is readily separated from the web that is wound and spreads into the working environment.
Moreover, the prior art devices restrict or at least hamper some operations that are necessary in the roll formation. One of these operations is the roll change wherein when the roll that is being wound becomes complete, a new roll spool must be fed into the gap between the winding drums, the web that is wound must be cut off, and the end of the cut-off web must be attached to the new roll spool. Thus, during roll change operations, various actuators are needed, such as web holders, cutting means, devices for the feed of a new roll spool, etc.